Defence Force Chief David Hurley says people smugglers would soon get around a policy of turning back asylum seeker boats.

The Federal Opposition insists that turning back asylum seeker boats when it is safe to do so would be a deterrent.

While General Hurley says Defence would discuss any change of policy with the Government of the day and enact it, he has told Sky News it would not work for long.

"They will work around this, I mean, we do things out on the water and that barrier effect there will change techniques and within two days they'll come up with a counter so they're very agile in that sense," he said.

In a wide ranging interview, General Hurley says he does not expect the Afghan government to be able to control some areas of the nation once western forces withdraw.

"There will be uncontrolled spaces as there always have been in Afghanistan," he said.

"There are desert areas in there where very few people live and there's no really point trying to conduct operations in there.

"But the major population centres around the ring road the major infrastructure in the country that's where they'll retain and maintain control."

General Hurley also confirmed about 10 people still serving in the military may have been involved in more than 20 alleged rapes at the Defence Force Academy in the 1980s and 90s.

However, he says the Defence Force Investigative Service is reviewing the evidence about those alleged rapes.

"I think it has been reported there are about 10 people that may be still serving, sorry, that are still serving and that's why the ADF investigative service is involved," he said.

General Hurley says the 10 people have not been stood aside - but the investigative process has started.

A task force is also separately considering whether to hold a Royal Commission into abuse in the Defence Force.